Automatic volume control circuits



June 21, 1938. G. L. BEERS AUTOMATIC VOLUME .CONTROL CIRCUITS 4 Sheets-Sheet l Filed Deo. 19, 1933 INVENTOR GEORG: L.BEERS 'BY/QQ ATTORNEY June 2l, 1938. L ERS C. 2,E20,999

ATOMATIC VOLUME CONTROL CIRCUITS Filed Dec. 19, 193s 4 sheets-sheet 2' GEORGE L. BEERS ATTORNEY June 21, 193s. G. L. BEERS 2,120,999

AUTOMATIC VOLUME CONTROL CIRCUITS Filed Deo. 19, 1935 4fSheets-Sheet 3 lNvENToR v GEORGE l.. BEERS G. L. BEERS AUTOMTIC IVLUME CONTROL CIRCUITS 4 sheds-sheet 4 Filed Dec. 19, 1933 INVENTOR GEORGE L BEERS ATTORNEY Patented June 21, 1938 AUTOMATIC VOLUMEA CONTROL CIRCUITSv George L. Beers, Collingswood, N. J., assigner to Radio Corporation of America, a corporation of Delaware Application December 19, 1933, Serial No. 703,034

17 claims.

My present invention relates to amplifier control arrangements, and more particularly to improved automatic `volume control systems for radio receivers.

Automatic volume control arrangements employed in the pastk have utilized gain control devices wherein a volume control rectifier output electrode assumed increasingly greater negative `potentials as the signal input to the receiver increased, It is one of the main objects of this invention toprovide an automatic volume control arrangement wherein precisely the reverse action takes place, the control rectifier output electrode swinging more positive with respect to the controlled amplifier cathode as the signal input to the rectifier increases.

Another important object of the invention is to provide an automatic volume control arrangement of the type utilizing a diode rectifier toI develop a direct current potential component from signals, the component being employed, however, to regulate the potential of the input grid of a tube which does not itself operate as a detector,

rectifier or signal amplifier, the gain of the high. frequency amplifier to be controlled being regu- C to provide improved automatic volume control yarrangements wherein the plate potential for the volume control tube Vcan be supplied from an alternating potential source.

An additional object of my invention is to provide improved automatic volume control arrangenientslof the type wherein the volume control tube has an alternating potential applied to its plate and the alternating current circuits already existing in the receiver are utilized to provide this plate potential, whereby a separate plate poten i tial source for the volume control tube is not re quired in either direct or alternating-current operated receivers.

-Another object of the invention is to provide an automatic volume control tube for a receiver wherein an alternating potential can beapplied to the control tube plate, the potential being derived from the oscillator circuit when the receiver is of the battery-operated, superheterodyne type, and from the conventional power supply transformer when the receiver is alternating-current operated.

An additional object of the invention is to provide an automatic Volume control system wherein the amplified signal voltage may be used as plate potential for the volume control tube.

(ci. 25o- 20) Still another object of the invention is to improve the existing and well-known types of automatic volume control arrangements for radio receivers, and particularly to provide satisfactory and economical arrangements of the type wherein an alternating potential may be applied to the automatic volume control tube.

The novel features which I believe to be characteristic of my invention are set forth in particu-- larity in the appended claims. The invention itself, however, both as to its organization and method of operation, will best be understood by reference to the following description, taken in connection with the drawings, in which I have indicated diagrammatically several circuit organizations whereby my invention may be carried into effect.

In the drawings:-

Fig. l shows one arrangement embodying the invention,

Fig. 2 shows a modification employing alternating current on the control tube plate,

Fig. 3 shows a modification of the arrangement of Fig. 2,`

Fig. 4 illustrates a modification employed in a battery-operated superheterodyne receiver,

Fig. 5 shows a further modification of the invention,

Fig. 6 illustrates still another modification.

Referring now to the accompanying drawings, wherein like reference characters in the different figures represent similar circuit elements, there is shown in Fig. 1 a conventional radio receiving system which embodies the automatic. volume control network of the present invention. amplifier tube l is disposed in a stage of tuned radio frequency ampliiicatiomrand it is to be clearly understood that this amplifier stage may vbe the intermediate frequency vamplifier of a superheterodyne receiver, or one of the tuned radio frequency amplifier stages of a cascaded tunable radio frequency amplifie-r receiver. The reference numeral 2 designates the source of signals which is coupled, as at M1, to the tuned input circuit 3 of the amplifier tube I; Of course, if the receiver is of the superheterodyne type then the network 2 will be understood to comprise the conventional networks which precede the intermediate frequency amplifier, and thesel commonly are a radio frequency amplifier coupled The more preceding stages of tuned radio frequency amplification.

Assuming that the receiver is of the superheterodyne type, the resonant circuitJ 3 is iixedly tuned to the operating intermediate frequency. The coupling transformer M2 in that case has its primary and secondary circuits each tuned to the operating intermediate frequency, while the detector tube, the second detector Ain the case of the superheterodyne receiver, is connected across the tuned circuit 4. In Fig. 1 the detector tube is shown as a diode 5, and the cold electrode, or anode, thereof is connected to the cathode through a path which includes -the tuned circuit 4 and a resistor 6 arranged in series, the resistor 6 being shunted by a radio frequency by-pass condenser 1.

The signal current impressed upon the circuit 4 develops across the resistor 6 an audio fre' quency signal potential component and a direct current potential component. The path which includes lead 8 and audio frequency signal coupling condenser 9 transmits the audio frequency signal component to one or more stages of audio frequency amplification, and the amplified audio frequency signal energy may then be reproduced in any desired manner. The lead 8 may terminate in an adjustable tap I0, and this tap may function as the manual volume control element of the receiver if desired. The direct current potential component of the detected signal current is impressed upon the control grid II of a screen grid tube I2 by connecting the grid I I through a lead I3 to the positive potential side of resistor 6. A potentiometer resistance P furnishes the operating direct current voltages for the electrodes of tubes I, 5 and I2, and only these circuits are shown in detail because they are the only ones that need be described for a clear understanding of the invention.' It is to be vclearly understood that the resistor PI is connected to the direct current power supply source, and that the latter may comprise any arrangement Well known to those skilled in the broadcast receiver art.

necting the anode of tube I2 to the point I 6;'

The cathode of amplier tube I is connected by lead Il to point I 8 on the potentiometer P, and a lead I9 connects the anode of tube I to point 2G which is at a more positive potential than the point I8'. The control grid of amplifier tube I is connected through a path which includes the lead 2'I and resistor 22 to the anode side of resistor' R. By-pass condensers are connected from either side of resistor 22 to point I8 of the resistor P.

The circuit relations between the various ele ments of the system shown in Fig. 1,` and the functions of the elements in the operation of the system will now be described. The direct current potential drop across resistor E is impressed upon the control gridy II of tube I2. The cathode i with respect to the point I4 to bias the tube I2 to, or beyond, the point of plate current cut-off in order to give the desired delayed automaticV volume control action. The resistor R is ncluded in the plate circuit of tube I2, and connects to point IB on the receiver B supply system, and this point is sufficiently positive with respect to the point I5 to give the desired plate voltage.

The cathodes of the controlled tubes, and speciically the cathode of tube I, are connected to point I3 on the potential supply resistor P, the direct current potential drop between the points IE- and I8 being utilized to provide the normal fixed bias for the controlled amplifier tubes. A resistance-condenser filter 22, 23, is provided between the plate side of resistor R and the controlled amplifier grid, or grids, to eliminate any audio frequency potentials which may appear in the plate circuit of tube I2.

When a signal is received the cathode of diode 5 becomes more positive with respect to the cathode of tube I2, and the grid bias of tube I2 is, therefore, reduced thereby causing an increase in the plate current flowing through resistor R. This results in an increase in the bias on the grids ofthe controlledl amplier tubes. Vhe'n no signals are received the negative bias on the grid II= of tube I2 is a maximum, and, therefore, there is a decreased flow of plate current through the resistor R, and the controlled amplifiers are operated at maximum sensitivity.

In Fig. 2 there is shown the circuit arrangement of Fig, l modified .in various respects. It will be noted'that the cathode' of tube I2 connects directly to the anode of the` diode detector tube fithrough'a lead 5'. The resistor 6 is connected to a point I4 on the potential' supply resistor P which is more negative than the point I4 to which the anode diode is connected. The control grid II ofv tube I2 v is connected to an intermediate point 6' on resistor 6. This arrangement results in a positive bias being applied to the anode of tube 5, and a negative bias being impressed on the grid I Irof tube I2.

Ifr the resistance between the cathode side of resistor 5 and point 6 is equal to the resistance between point E and point I4', the bias on the control grid I-I4 will be approximately half the potential drop between points I4 and I4. The change in the control grid bias of tube I2 with an increase in the strength-of the signal applied to diode 5 will be approximately half that ob* tained from the arrangement shown in Fig. l. The resistor R in the plate circuit of tube I2Y in Fig. 2 returnsdirectly to the cathode of the tube, the plate potential for the tube being provided through the secondary winding of the 60 cycle alternating current transformer M3. The use of the alternating current plate potential for tube l2* makes it unnecessary to provide the plate potential for this tube-from the V supply system of the receiver. Since the platel supply for the automatic volume control system and the ampli- Iier tubes must normally beconnected in series, the use of alternating eiurent onA the plate of tube I2 makes it possible to reduce the total potential which the receiver B supply system must provide by the voltage normally used for tube I2. The screen grid of tube I2- can, of course, connecttothe B supply system in parallel with the screen grids of the other amplifier tubes.

The resistance-condenser filter IFM-J2', inserted between point 6 and the input electrodes of tube I2r in Fig. 2, functions to prevent audio frequency potentials being applied to the control grid of tube l2. This filter can likewise be employed in the arrangement shown in Fig. l. While the diode 5 in Fig. 1V is shown as functioning additionally as the second detectorfof the re-V ceiver, in Fig. l a separate audio detector must be used because of the positive bias which is ap `same tube envelope as the electrodes of the automatic volume control diode 5. Those skilled in the art are well aware of multi-function tubes which can accomplish this purpose, and it is pointed out that a common cathode could then be used for the two diode anodes, one of the diode anodes functioning for the automatic volume control 'system as in Fig. 2, and the other diode anode functioning as the audio demodulator as shown in Fig. l. The advantages of thearrangement shown are as follows:-

In Fig. 2 the anode of the rectier 5 which is coupled to the output of the amplifier connects directly to the cathode of the tube I2. In both arrangements the output electrode of the rectiiier becomes less negative with respect to the cathode of the tube. or tubes which the rectifier'Y controls as the signal strength increases. This is dis* tinctly contrary to automatic volume control methods employed heretofore wherein the output electrode of the automatic volume control rectifier becomes more negative with increase in signal strength with respect to the controlled am plifier cathodes.

The plate potential for the tube I2 in both arrangements can be supplied from an alternating current source, and thereby minimize the voltage requirements of the receiver B supply system.

Either arrangement provides a large change in control grid bias on the controlled'amplifler tubes for a small increase in signal strength due to the high direct current component amplification provided b-y tube I2. In a previous automatic volume control system, in which the plate potential of a triode was supplied from an alternating current source and the signal was applied to the control grid, difficulty was encountered when a signal was received which was modulated with 60 cycles and the modulation was degrees out of phase with the applied plate voltage. Under these conditions no automatic volume control action was obtained. With the present arrangements this difficulty is overcome since only variations in the direct current potential derived from the control diode are applied to the control grid of the tube which is supplied with the alternating current plate potential. y

In Figs. 3 and 4 are shown two further modications of the present invention, both of these modications utilizing the essential mode of opn eration disclosed in Fig. 2. The alternating cur-` rent potential utilized for the plate of tube I2 in Fig. 2 may be developed by the local oscillator of the superheterodyne receiver, or it may be derived from another source such as the power transformer in an alternating current operated receiver. In Fig. 3 the plate potential `of tube I2 is supplied from the secondaryv 3|! of the power transformer T through the coupling condenser 3|. The transformer T is of a conventional and well known form, and its primary winding is connected to the usual 60 cycle alternating current source. The secondary winding 3l] is oonnectad to the usual full wave power "rectifier,

the mid-tap of the secondary winding being connected to the negative side of the bleedei` resistor P. Only such details of the power supply circuit arrangement as are essential to an understanding of the present shown, the remaining details being well under stood by those skilled in the art.

In Fig. 2 the plate potential for tube I2 is supplied through a special winding on the power transformer, the special winding being connected in series with the plate of the tube. However, in Fig. 3 the secondary winding of the power transformer itself is utilized for supplying the potential for plate I2, the alternating current potential being applied through the condenser 32. The diode control tube 5 has its anode connected to point I4, the diode functioning not only as a control rectifier for the automatic volume control system, but also as the audio demodulator, and its circuits are arranged as shown in Fig. l. The anode of tube. I2 is connected through the resistor R. to point it on vthe bleeder resistor P, and it will be noted that this point is more negative than the point I5 to which the cathode of tube I2 is connected. It should also be noted that they cathode of the controlled amplier is connected by lead Il directly to the cathode of tube I2. The actual electrodes of the controlled amplier stage have been omitted, and only the direct current connections from the bleeder resistor P and the tube I2 are shown. This same connection arrangement may be employed in connection with Fig. 2 wherein the alternating current plate potential is provided by the series winding arrangement.

invention are plate circuit of tube I2 is connected to point I6 which is more negative than point I5 because there is thus provided the properkxed bias on the controlled amplier tube since the cathodes of the tube I2 and the controlled amplifier tube are "connected to the common point I5.

The tube I2 is a screen grid tube, the screen being connected to point il on the bleeder resistor P, and preferably is of the pentode type. If the plate potential for tube I2 is supplied fromv 'the local oscillator of the receiver, the applied Aplate potential may vary through the tuning range of the receiver, or with variations in tubes, etc. Since the operating characteristics of the pentode tubes are reasonably independent of the applied plate potential, the effects of these variations will not be serious. Of course, a pentode tube may also be utilized for the tube i2 in Fig. 2.

In Fig. 6 there is shown a variation of the arrangement shown in Fig. 3, and it will be noted that the difference between the two arrangements resides in the fact that in Fig. 6 both the cathodes and control grids of the amplier tubes being controlled are connected to the bleeder resistor P so that they are always negative with respect to any of the rectier electrodes. This is permitted through the use of the alternating potential on the plate of the automatic volume control tube. Since the circuit elements in Fig. 6 are substantially the same as those shown in Fig. 3, similar reference numerals are utilized, but in Fig. 6 these reference numerals are associated with prime designations. It will be ob served that the control grid II of the volume control tube I2 is connected to the cathode side of resistor 6', while the negative side of resistor I is connected to point Id on the bleeder resistor P. the arrangement of Fig. 6 the diode anode is Furthermore, it will be noted that in l connected to the high alternating current. potential` side of the tuned input circuit. of diode 5', whileV the cathode of the diode is connected to the controlv grid` side of resistor The rey sistor R is'connected between the anode of tube l2 and point I6', which is now at a more negative potential than the,y point |41. Additionally, the lead 40', instead of being connected to the cathode point I5', is connected to a point I6 which is at a potential intermediate the potentials of points I6 and I4.

The arrangement of Fig. 4 shows the same general arrangement of Fig. 3 applied to a battery operated receiver. The diode 5 must be provided with; anindirectly heated cathode, and

all the other tubes in the receiver may be of the lament type and can be operated from a common source ofv iilament potential. The plate potential for tube l2,is supplied through coupling condenser 50 from the tunable circuit 5| of the local oscillator. In other words, it is to-be clearly understood that the receiver shown in Fig. 4 is of the superheterodyne type, and that the circuit 51 is connected i-n the local oscillator stage of the receiver.

The details of, the local oscillator stage are not included, because. they are not essential to a proper understanding of the present invention, one side of the circuit 5I being shown grounded, and the high alternating current potential side being'shown connected through condenser 5B to the plate of tube l2;

The variable condenser 52 functions as the tuning means of the local oscillator stage, and those skilled in the art are well aware of the manner of constructing a receiver oi this typ-e. By means of the arrangement shown in Fig. 4 a battery operated receiver can be equipped with an amplified automatic volume control system .which does not require the use of an additional source of plate potential. It is believed that the remaining constructional details of Fig. 4 will be readily understood from the arrangement shown in Fig. 3. The diode 5 functions both as a control rectiiier and as an audio demodulator, the anode of diode 5 being connected to the negative terminal of the biasing source C, and the cathode of` tube l2 being connected to the positive terminal of the C bias source.

The volume control resistor Ris connected between the plate of tube l2 and the plate of the diode 5, the grid of the controlled radio frequency amplifier being connected to the plate side of resistor R. The resistance-condenser filter 22', 23' is employed to prevent audio frequency pulsations from affecting the controlled amplifier, and is disposed` in the automatic volume control arrangement. Tubes 5 and I2, both in Figs. 3 and` 4, can be combined in` a single tube envelope if desired. Additionally, a small copper oxide rectifier may be substituted for the rectifier 5 in either of Figs. 3 or 4.

In Fig. 5 is shown a modilication of the present invention which is based upon a combination of the arrangement shown in Figs. 1 and 3. In this form of the invention the alternating potential for the automatic volume control tube is provided by the received signal. The tube 60 has its grid circuit coupled tothe grid of tube l through a small signal coupling condenser 6|;

The received signal is ampliedby tube 6U, and applied to the plate of the automatic volume control tube |2 through the coupling transformer M4. In case sufficient voltage is not ldeveloped across ,the oscillator, tuned circuit in somev battery. operated receivers, the` arrangement shown in Fig. 5` may be used to advantage.

In any of the automatic volume control arrangements shown herein the determining factor in the plate potential which is required` for the volume control tube is the amount of bias which will be necessary to provide sufficient control for the strongest signal which the. receiver must handle. With` the arrangement shown in Fig. 5 the plate potential for the volume control tube l2 automatically increases as the signal increases so the necessary plate potential is always available to provide the required bias voltage. This is accomplished specifically by connecting the plate of tube l2, as through a lead 62, to one side of the secondary winding 63 of transformer M4, the opposite side of winding 63 being connected by lead 64 to the negative side of resistor R. It will be noted that the reference `numerals employed in Figs. 1 and 3 are employed in Fig. 5 Y

and this is done because such similarly designated elements correspond to circuit elements of these figures.

While I have indicated and described several systems for carrying my invention into effect, it

will be apparent to one skilled in the art that my invention is by no means limited to the particular organizations shown and described, but that many modifications may be made without departing from the scope of my invention, as set forth in the appended claims.

What I claim is:-

l. In a radio receiving system, a signal-responsive device for deriving unidirectional potentials proportional to the amplitude of received signals, an alternating potential source, means for deriving unidirectional biasing potentials directly from said alternating potential source, and connections between said device and deriving means of such polarity that the said biasing potential deriving means is controlled by the potentials derived from the signal-responsive device in a sense to increase said biasing potentials when the received signal amplitude increases.

2. In a radio receiving system, a high frequency potential source, a low frequency potential source, a device for deriving unidirectional potentials from said first-mentioned source, means for deriving uni-directional biasing potentials from said low frequency source, and connections between said source and deriving means of such polarity that the amplitude. of the second-mentioned unidirectional potentials is controlled by the first-mentioned unidirectional potentials in a sense to increase the biasing potential amplitude with increase of high frequency potential.

3. In a radio receiving system, an amplifier tube, a diode coupled to said amplier tube, an automatic volume control tube having an input electrode, a cathode an-d an output electrode, a unidirectional potential source, a direct current connection betweenA the cathode electrode of the diode and the input electrode of the automatic volume control tube, connections to said unidirectional potential source whereby the cathode of the automatic volume control tube is-normally maintained at a positive potential with respect tothe cathode electrode of the diode, means for connecting the amplifierl cathode to a potential point on said source which is positive with respect to the dio-de cathode potential and which is at least as positive asthe-control tube cathode whereby when; anincoming signal is, impressed4 2,120,999 'upon the diode, the cathode of the amplifier tube becomes more positive with respect to the cathode electrode of the diode, and a separate potential source for supplying plate potential to the automatic volume control tube.

4. In combination, a controlled amplifier, a diode demodulator having a signal input circuit connected between its cathode and anode, an impedance in the space current path of the diode circuit including a relatively fixed direct current potential point, a second point on said impedance in the demodulator circuit which is at a direct current potential adapted to increase positively with respect to the first point as the intensity of signals impressed on the demodulator circuit increases, said impedance being in a series path with the diode electrodes and said signal input circuit, and means connecting said second point to the input circuit of the controlled arnplifier in such a manner that the gain of the controlled amplifier decreases with said signal intensity increase, sai-d last named means including a tube having its control grid connected to said second named point and its anode connected to the amplifier input circuit through a direct current connection, the cathode of the last tube being at a positive potential with respect to the f potential of the said second point.

5. In combination, a controlled amplifier, a diode demodulator circuit including a resistor in its space current path, the resistor having a relatively fixed direct current potential point, a second point on the `resistor in the demodulator circuit which is at a direct current potential adapted to increase positively with respect to the first point as the intensity of signals impressed l on the demodulator circuit increases, said demodulator circuit having a signal input network, and the resistor being in a series path with the network and diode electrodes, and means con necting said second point to the input circuit of the controlled amplifier in such a manner that the gain of the controlled amplifier decreases with said signal intensity increase.

6. In combination, a controlled amplifier, a demodulator circuit including an impedance in its space current path having a relatively fixed direct current potential point, a second point on the impedance Ain the demodulator circuit which is at a direct current potential adapted to increase positively with respect to the first point as the intensity of signals impressed on the demodulator circuit increases, and means connecting said second point to the input circuit of the controlled amplifier in such a manner that the gain of the controlled amplifier decreases with said signal intensity increase, said last named means including an electron discharge tube, additional means for impressing an alternating current between the anode and cathode of said tube, and means responsive to potential variations of the second point for varying the space current fiow of said last tube. y

7. In an automatic volume control system for a radio receiver, a diode rectifier having a signal input circuit connected in series between the diode cathode and anode, a controlled high frequency amplifier having its output circuit coupled to said rectifier input circuit, a control tube, means for connecting the control grid of said control tube to the cathode side of said rectifier input circuit which is adapted to increase in a positive direction in direct current potential as signals are impressed upon said demodulator circuit, and a direct current connection between the anode of said control tube and an input electrode of'saidcontrolled amplifier.

8. In an automatic volume control system for a radio receiver, a diode kdernodulator circuit, a controlled high frequency amplifier having its output circuit coupled to said demodulator circuit, a control tube, means for connectingthe control grid of said control tube to a point in said demodulator circuit which is adapted to increase in a positive direction in direct current potential as signals are impressed upon said demodulator circuit, a direct current connection between the anode of said control tube and an input electrode of said controlled amplifier, and a source of alternating current potential coupled to the anode circuit said control tube for rectification, an impedance in the controltube anode circuit developing an amplifier gaincontrol bias from the rectified current.

9. In an automatic volume control system for a radio receiver, a diode dernodulator circuit, a controlled high frequency amplifier having its output circuit coupled to said dernodulator circuit, a control, tube, means for connecting the control grid of said control tube to a point in said demodulator circuit which is adapted to increase in a positive direction in direct current potential as signals are impressed upon said demodulator circuit, and a direct current connection between the anode of said control tube and an input electrode of said controlled amplifier, a source of alternating current potential including a power supply transformer, means for coupling the anode circuit of said control tube to the transformer secondary winding 10. In an automatic volume control system for a radio receiver, a diode rectifier circuit, a controlled high frequency amplifier having its out put circuit coupled to said rectifier circuit, a control tube, means for connecting the control grid of said control tube to a point in said rectifier circuit which is adapted to increase in a positive direction in direct current potential as signals are impressed upon said rectifier. circuit, and a direct current connection between the anode of said control tube and an input electrode of said controlled amplifier, a local oscillator circuit included in said receiver, and an` oscillation coupling path between the anode circuit of said control tube and said local oscillator circuit. l1. In ra radio receiver, va high frequency amplifier, a diode rectifier, a gain control tube, a resistor connected between the anode and cathode of the rectifier, a signal circuit having its high alternating current potential side connected to the diode cathode and its low alternating current potential side connected to the diode anode throughsaid resistor, means for connecting the control grid of the gain control tube to the cathode side of said resistor, a direct current connection between the anode of the gain control tube and the input circuit of said high frequency amplifier, and a direct current potential source con-- nected to the electrodes of said diode rectifier and gain control tube.

12. In a radio receiver, a high frequency amplifier, a diode rectifier, a gain control tube, a

resistor connected between the anode andcathode of the rectier, a signal circuit having its' nection between the anode of the gain control tube and the input circuit of said high frequency amplier, a direct current potential source connected to electrodes of said diode rectifier and gain control tube, and a source of alternating current potential coupled to the anode circuit of said gain control tube for rectification of the alternating current, the intensity of the rectiiied current being dependent upon the potential value of the cathode side of said resistor.

13. In a signalling system, in combination, a vacuum tube amplifier having a cathode and a control electrode, a vacuum tube detector coupled directly to the output -of said amplier, said detector havin-g a cathode and an anode, means for normally maintaining said detector cathode at a negative potential with respect to said amplifier cathode,.means for normally maintaining the detector anode at a negative potential with respect to said amplifier cathode, means -whereby an ine comingsignal causes said detector cathode to become more positive, a source of alternating current energy, a rectifier for said energy, a connection between the detector cathode and :an electrode of the rectifier for regulating its conductivity, and a connection between said rectiiier and the control electrode of lsaid vacuum -tube ampliiier for impressing `rectified energy upon the latter.

14. In a signalling system, in combination, a vacuum tube ampliiier having a cathode -a-nd a control electrode, a vacuum tube detectorcoupled directly to the output of said amplifier, said vdetector having a cathode and an anode, means -for normally maintaining said detector cathode Aat a negative potential with respect to said amplifier cathode, means for normally maintaining the detector anode at a negative potential with respectto said amplier cathode,means whereby an incoming signal causes said detector cathode to become more positive, a source -of alternating current energy, a rectifier for said energy, =a connection between the detector cathode and an electrode of the rectifier for regulating its' conductivity, and a connection between said recti- Iier and lthe'control electrode of said vacuum tube ampliiier for impressing rectifier energy upon the latter and said alternating current source comprising the 60 cycle power supply source of the system.

l5. In a signalling system, `in combination, a vacuum tube amplifier having a cathode and a 4control electrode, a vacuum tube detector coupled directly to the output of said ampliiier, said detector having a cathode and an anode, means for normally maintaining said detector cathode at a negative potential with respect to said amplifier cathode, means for normally maintaining the detector anode at a negative potential with Arespect to said Vampliiier cathode, means whereby an incoming signal causes said `detector cathode to become more'positive, a'source of alfternating current energy, a rectier for said `energy,a connection between the detector cathode yand an electrode of the rectiiier for regulating its conductivity, wand alconnection between said rectier and-thecontrolelectrode of said vacuum tube amplier for impressing rectified energy'upon the latter, and 'said alternating source comprising a network cou-pled to said amplifier.

Ilo. In combination with a high frequency signal transmission tube,l an oscillator arranged to produce electrical wave energy, a rectifier connected to said oscillator to produce ra direct cur rent voltage component solely from saidelectrical waves, means for impressing the said component upon the tubeto control the gain thereof, vand means for controlling the eiiciencyof rectification of said Waves by said rectifier in response to received signal 'amplitude variations.

17. vA-method of controlling the gain'of asignal transmission tube coupled vto a demodulator which consists in 4producing local oscillation kwave energy, rectifying solely the said energy, v.regulating the rectiiication `of saidlenergy in response to lreceived signal amplitude variations, and impressing solelyy the `recti-iied'wave energy upon the transmission -tube to regulate the gain thereof.

GEORGE L. BEERS. 

